Re: [PATCH v2 2/4] x86, boot: PUD VA support for physical mapping (x86_64)

Dave Hansen
2016-05-02T21:58:08Z

On 05/02/2016 02:41 PM, Thomas Garnier wrote:
> Minor change that allows early boot physical mapping of PUD level virtual
> addresses. This change prepares usage of different virtual addresses for
> KASLR memory randomization. It has no impact on default usage.
...
> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
> index 89d9747..6adfbce 100644
> --- a/arch/x86/mm/init_64.c
> +++ b/arch/x86/mm/init_64.c
> @@ -526,10 +526,10 @@ phys_pud_init(pud_t *pud_page, unsigned long addr, unsigned long end,
> {
> unsigned long pages = 0, next;
> unsigned long last_map_addr = end;
> - int i = pud_index(addr);
> + int i = pud_index((unsigned long)__va(addr));
>
> for (; i < PTRS_PER_PUD; i++, addr = next) {
> - pud_t *pud = pud_page + pud_index(addr);
> + pud_t *pud = pud_page + pud_index((unsigned long)__va(addr));
> pmd_t *pmd;
> pgprot_t prot = PAGE_KERNEL;

pud_index() is supposed to take a virtual address. We were passing a
physical address in here, and it all just worked because PAGE_OFFSET is
PUD-aligned. Now that you are moving PAGE_OFFSET around a bit and not
PUD-aligning it, this breaks. Right?

Could you spell this out a bit more the changelog?